FILE - In this Feb. 19, 2013 file photo Cecilia Rutherford joins a group of protesters outside Hurley Medical Center in Flint, Mich., after a nurse filed a complaint against the hospital claiming it had agreed to a man's request that no African-American nurses care for his newborn. The case involving a white swastika-tattooed Michigan father and a black nurse at the hospital highlights one of medicine's ?open secrets? _ allowing patients to refuse treatment by a doctor or nurse of another race. The nurse is now suing the hospital, claiming it bowed to his illegal demands. (AP Photo/The Flint Journal, Lauren Justice, File) LOCAL TV OUT; LOCAL INTERNET OUT

President Obama argued Friday for keeping a key provision of federal voting rights law in place, saying that if the Supreme Court strikes down that part of the law, it will become harder to help people who believe their rights at the polls have been violated.

The court has scheduled oral arguments for Wednesday on a challenge from Shelby County, Ala., near Birmingham, to a section of the Voting Rights Act. The provision requires all or parts of 16 states with a history of racial discrimination, mostly in the South, to get approval from the Justice Department or federal court in Washington before making any changes in the way they hold elections, such as moving a polling place.

The appeal argues that places covered by the law have made such progress that Washington oversight is unnecessary. Opponents of the provision point out that in the decades since the landmark law was enacted in 1965, so much racial progress has been made that the U.S. elected and re-elected Obama, the country's first black president.

Defenders of the provision say that it's still needed, particularly in light of efforts in many states to impose new requirements on voters, such as shortening the window for early voting or requiring voters to show photo identification before they cast a ballot. Some say those requirements disproportionately affect blacks and other racial minorities.

In a radio interview broadcast Friday, Obama said removing the oversight requirement would make it harder for voters who believe their rights have been violated to get relief. He said the change would mean that such voters would have to wait until potential obstacles were actually put in place before they could then attempt to have them overturned, rather than challenging them before they were imposed.

"So generally speaking, you'd see less protection before an election with respect to voting rights," Obama said in the interview with SiriusXM host Joe Madison. "People could keep on coming up with new schemes each election. Even if they were ultimately ruled to violate the Voting Rights Act, it would be hard for us to catch those things up front to make sure that elections are done in an equitable way."

The federal requirement for advance approval was adopted to give federal officials a potent tool to defeat persistent efforts to keep blacks from voting. The provision has been a huge success, and Congress periodically has renewed it over the years. The most recent occasion was in 2006, when a Republican-led Congress overwhelmingly approved a 25-year extension and President George W. Bush signed it.